Methods of preparing radiation resistant heat sealable polymer blends

ABSTRACT

Polymer blends of non-crystalline mesomorphous polypropylene and a polymer compatible with such polypropylene and the method of making such polymer blends are provided. Such compatible polymer blends exhibit substantial maintenance of structural integrity after exposure to gamma irradiation and provide heat sealing properties, puncture resistance, and tear strength. Films, fibers, and other articles made from such blends may be used in various applications, including medical articles such as medical packaging films, ostomy pouches, and transdermal delivery patches, which may require sterilized storage prior to usage.

This is a division, of application Ser. No. 07/371,713 filed Jun. 26,1989, now U.S. Pat. No. 5,140,073.

Field of the Invention

This invention relates to polymer blends of compatible polymersresistant to the effects of sterilization irradiation, methods forpreparing such polymer blends, and articles, such as fibers, films, andnonwoven fabrics incorporating such polymer blends. More particularly,this invention relates to polymer blends of non-crystalline mesomorphouspolypropylene and polymers compatible with such polypropylene. Films ofsuch blends may be used as heat sealable packaging for medical articlesrequiring sterilized storage, heat sealable backings for transdermaldelivery medical packaging, or as heat sealable components for use asostomy pouches also possibly requiring sterilized storage.

BACKGROUND OF THE INVENTION

Polypropylene is often a material of choice for medical articles due toits various properties such as non-toxicity, chemical resistance andinertness to drugs and liquid media used with drugs, as well as its lowcost and ease of processing by means of extrusion, molding, and thelike.

However, a disadvantage of crystalline polypropylene is its inherentinability to be heat sealed against another material. Medical articlesor packaging for medical articles often require heat sealing in themanufacturing process to assemble the components of the article or thepackaging process to protect the active ingredient or medical article inthe packaging from undesired exposure.

Medical articles requiring additional protection beyond secure heatsealing in manufacturing or packaging processes can be sterilized at thetime of production and thereafter maintained in a sterile conditionduring storage. Not all medical articles require sterilization prior tousage. But structural components resistant to radiation are moreversatile for uses in medical articles and packaging than componentsunable to maintain structural integrity after irradiation. Thus, themost desirable material for a medical article or the packaging thereforis one which possesses resistance to the structurally demanding forms ofsterilization even if current usages of the medical articles do notrequire such sterilization.

A preferred method of sterilization uses gamma radiation, such asradioactive cobalt 60, since it can be performed on packages sealed byheat or other methods insuring total and reliable sterility of thecontents

Unfortunately, gamma-irradiation of crystalline polypropylene causesdegradation of its structural integrity (e.g., causing embrittlement,discoloration, thermal sensitivity).

To avoid such degradation, the prior art has employed a variety ofstabilizers and other additives. European Patent Publication 0248545(assigned to the same assignee as for this application), the prior arttherein described the efforts undertaken to stabilize crystallinepolypropylene from degradation after irradiation.

Conversely, mesomorphous, non-crystalline polypropylene, as described inEuropean Patent Publication 0248545, provides resistance tosterilization irradiation without the necessity of any additive orstabilizer. Control over the method of preparing such mesomorphouspolypropylene causes such polypropylene to substantially maintain itsstructural integrity after sterilization irradiation.

Unfortunately, films for packaging and the like made from polypropylene,even non-crystalline mesomorphous polypropylene, are susceptible totearing and puncturing that disrupt maintenance of structural integrityas a manufactured product or packaging component after assemblyUsefulness of a sterilized medical article is compromised by a puncturein a polypropylene package. Also, as described above, crystallinepolypropylene is not a material which can be heat sealed against anothermaterial in order to provide either a multi-component medical article oran effective radiation sterilized package.

On the other hand, polybutylene, poly(1-butene) or poly(2-butene) orboth, offers many advantages to the medical packaging art thatpolypropylene, mesomorphous or otherwise, lacks. Polybutylene has hightear strength, high impact strength, puncture resistance. Polybutyleneis also often used as a film requiring heat sealability. Reference tothe versatility of polybutylene may be found in Shell Technical Bulletinsc: 391-79 (1979). However, polybutylene is highly crystalline (as muchas 98% crystalline). After irradiation, the melt index of polybutylenehas increased, indicating chain scission. See Bradley, Journal ofIndustrial Irradiation Technology (2) 93-138 (1984). Hence, polybutylenepackaging usually degrades over the effective storage life often neededfor a medical product.

Neither crystalline polyproylene nor crystalline polybutylenesubstantially maintain structural integrity after sterilizationirradiation. Mesomorphous polypropylene lacks desirable strengthpackaging properties. No single polymer combines radiation resistanceand several good packaging properties, e.g. tear strength, punctureresistance, and heat sealability.

Thus, what is needed is a heat sealable medical packaging materialhaving good strength which substantially maintains its structuralintegrity for a useful period, even after exposure to the irradiationdosages necessary to sterilize such material.

SUMMARY OF THE INVENTION

The present invention overcomes the deficiencies of crystallinepolypropylene, crystalline polybutylene and mesomorphous polypropylenefor medical articles or their packaging by providing a polymer blendwhich has good tear strength, puncture resistance, and heat sealablityagainst another material and which substantially maintains itsstructural integrity over a useful life, even after irradiation. Suchpolymer blends comprise non-crystalline mesomorphous polypropylene andat least a discernible amount of a polymer "compatible" withnon-crystalline mesomorphous polypropylene.

This invention concerns polymer blends of non-crystalline, mesomorphouspolypropylene and a "compatible polymer".

For purposes of this invention, the definition of "polymer" includes ahomopolymer, an oligomer, a mixture of a homopolymer and an oligomer, amixture of more than one homopolymer, a mixture of more than oneoligomer, a mixture of a homopolymer and a plurality of oligomers, amixture of an oligomer and a plurality of homopolymers, or a mixture ofa plurality of homopolymers and a plurality of oligomers.

The definition of "compatible" is material for an understanding of thepresent invention. Those skilled in the art, such as Sonja Krause in herarticle, "Polymer-Polymer Compatibility" appearing as Chapter 2 inPolymer Blends, Paul and Newman, Ed., Academic Press, New York, 1978, atpages 16-18, recognize several possible definitions of compatibility ofpolymers, some based on the miscibility, on a molecular scale, ofhomopolymers and of random copolymers. One of the definitions ofpolymer-polymer compatibility is that the polymer mixtures havedesirable physical properties when blended.

For purposes of this invention, a blend comprising non-crystallinemesomorphous polypropylene and a "polymer compatible with saidpolypropylene" is a blend that at least one weight fraction has a moredesirable specific physical property, a greater percent elongation atbreak value, than the hypothetical percent elongation at break valuecomputed by the sum of the proportionate elongation at break values ofthe constituents of the blend according to the following equation:

Hypothetical percent elongation at break=((Weight percent ofmesomorphous polypropylene in the blend)×(Percent Elongation at Break ofmesomorphous polypropylene))+((Weight percent of polymer in theblend)×(Percent Elongation at Break of the polymer)).

Expressed in other words, "compatibility" of a "polymer compatible withsaid polypropylene" mixed with non-crystalline mesomorphouspolypropylene in a blend exists at any specific blended weight fractionwhen the percent elongation at break of that blend of the polymers isgreater than the hypothetical value established by plotting a straightline between the percent elongations at break of the respectivepolymers. Graphic representations of polymer-polymer compatibility ofseveral blends of the present invention are described in the Embodimentsof the Invention.

It is desirable, but not necessary, for a blend of the present inventionto have a consistently greater percent elongation at break value ascompared with the hypothetical linear value of the percent elongation atbreak for the blends across a variety of weight fraction. But it isnecessary within the scope of the present invention to have at least oneblend weight fraction have a percent elongation at break value which isgreater than the hypothetical linear value for that blend weightfraction.

The percent elongation at break property for polymer blends is chosen asthe physical property for determination of compatibility because it isthe best measurement to record the effects of irradiation of the polymerblend. A polymer blend which does not substantially maintain itsstructural integrity during at least two months after sterilizationirradiation begins to rapidly degrade or embrittle. Percent elongationat break measures the extent of degradation or embrittlement. Asubstantially constant percent elongation at break measured over severalmonths after irradiation is indicative of substantial maintenance ofstructural integrity of a polymer blend over that period afterirradiation.

The invention further provides a method for the preparation of thepolymer blend by the blending of polypropylene and a polymer compatibletherewith, extruding such blend of polymers, quenching such extrudedpolymer blend immediately after extruding to provide a mesomorphouspolymer blend having non-crystalline mesomorphous polypropylenecontained therein.

The present invention describes and utilizes a blend of non-crystalline,mesomorphous polypropylene with a polymer or polymers compatible withsuch polypropylene. These blends optimize the combined physicalproperties of resistance to radiation, if needed, provided by suchnon-crystalline, mesomorphous polypropylene with other desirable medicalpackaging properties not found in polypropylene but provided by thecompatible polymer, e.g. toughness, puncture resistance, and the like.

For an additional appreciation of the scope of the present invention, amore detailed description of the invention follows, with reference tothe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph comparing percent elongation at break values forExamples 1-5 with hypothetical linear values for Examples 1-5.

FIG. 2 is the x-ray diffraction pattern of crystalline polybutylene ofExample 1.

FIG. 3 is the x-ray diffraction pattern of the polymer blend of Example2.

FIG. 4 is the x-ray diffraction pattern of the polymer blend of Example3.

FIG. 5 is the x-ray diffraction pattern of the polymer blend of Example4.

FIG. 6 is the x-ray diffraction pattern of non-crystalline mesomorphouspolypropylene of Example 5.

FIG. 7 is a graph comparing percent elongation at break values forExamples 16-19 with hypothetical linear values for Examples 16-19.

FIG. 8 is the x-ray diffraction pattern of the polymer blend of Example16.

FIG. 9 is the x-ray diffraction pattern of the polymer blend of Example17.

FIG. 10 is the x-ray, diffraction pattern of the polymer blend ofExample 18.

FIG. 11 is the x-ray diffraction pattern of the polymer blend of Example19.

EMBODIMENTS OF THE INVENTION

The polymer blends of compatible polymers of he present inventionsubstantially maintain their structural integrity for a useful periodafter irradiation. The blends are produced from non-crystallinemesomorphous polypropylene blended with a polymer compatible with suchpolypropylene.

As described above, compatibility of a polymer with non-crystallinemesomorphous polypropylene is determined by a comparison of the percentelongation at break of a weight fraction of a blend with thehypothetical value of percent elongation at break at that weightfraction as determined by the respective blended polymers in theirproportionate weight fraction.

Graphically, the determination of a blend of a "compatible polymer" andnon-crystalline mesomorphous polypropylene is apparent from anexamination of FIG. 1, depicting the unirradiated, zero duration resultsfrom Table I below. The percent elongation at break of each example ofthe blend is greater than the hypothetical value of the percentelongation at break for that blend in that weight fraction. Therefore,each of the weight fractions of the blends is a mixture ofnon-crystalline mesomorphous polypropylene and a "polymer compatiblewith said polypropylene".

The number of polymers compatible with the non-crystalline mesomorphouspolypropylene appear limited. It has been found that polymers compatiblewith non-crystalline mesomorphous polypropylene include polybutylene(melt index from about 0.4 to about 100); and certain polyolefinelastomers produced by Exxon Corporation, such as Exxelor PA-23, whichis believed to be an ethylene based elastomer; This list of polymers isnot necessarily exhaustive of polymers compatible with mesomorphouspolypropylene as "compatible" is defined herein.

The optimum weight fraction of the compatible polymer with themesomorphous polypropylene depends upon the ultimate intended use of theblend and the desired properties. Generally, it is desirable to add asmuch compatible polymer as possible to provide strength, heatsealability, and other packaging properties without compromising theradiation resistance provided by the mesomorphous polypropylene.

However, it is within the scope of this invention to add a discerniblyminimal amount of the compatible polymer to mesomorphous polypropyleneto provide a blend quenched to preserve mesomorphous polypropylene,having excellent sterilization irradiation resistance and betterphysical properties such as elongation at break than the mesomorphouspolypropylene homopolymer. If the polymer blend having a minimal weightfraction of the compatible polymer can be discerned to have a greaterpercent elongation at break value than the hypothetical linear valuecomputed according the equation described in the Summary of theInvention above, then the polymer blend is within the scope of thisinvention.

Optionally, as little as one percent by weight of the compatible polymerto the weight of the polymer blend, quenched to preserve mesomorphouspolypropylene, may form an acceptable polymer blend for certain medicalpackaging devices to provide a radiation resistant blend having somedesirable packaging properties.

It is within the scope of this invention to add a discernibly minimalamount of polypropylene to the compatible polymer to provide a blend,quenched to preserve mesomorphous polypropylene, having excellentmedical packaging properties and acceptable radiation resistance.Analogously, if the polymer blend having a minimal weight fraction ofmesomorphous polypropylene can be discerned to have a greater percentelongation at break value than the hypothetical linear value computedaccording to the equation described in the Summary of the Inventionabove, then the polymer blend is within the scope of this invention.

Optionally, as much as ninety-nine percent (99%) by weight of thecompatible polymer to the weight of the polymer blend, may form anacceptable blend for certain medical packaging purposes.

Desirably, the weight fraction range of the compatible polymer is fromabout five percent (5%) to about ninety-five percent (95%) by weight ofthe compatible polymer to the weight of the polymer blend and moredesirably from about ten percent (10%) to about ninety percent (90%) byweight of the compatible polymer to the weight of the polymer blend.

Preferably, for balance of the best properties of mesomorphouspolypropylene and the compatible polymer in the blend, a weight fractionof the compatible polymer ranges from about twenty percent (20%) toabout eighty percent (80%) by weight of the compatible polymer to theweight of the polymer blend, more preferably from about twenty-five(25%) to about seventy-five percent (75%) by weight of the compatiblepolymer to the weight of the polymer blend, and most preferably fromabout forty percent (40%) to about sixty percent (60%) by weight ofcompatible polymer to the weight of the polymer blend.

Totally optionally, to provide specific additional properties to thepolymer blend, the polymer blends of the present invention may alsocontain conventional additives such as antistatic materials, pigments,dyes, plasticizers, ultraviolet absorbers, nucleating agents, quenchingagents such as mineral oil in weight fractions to the polymer blend ofabout 30-40 percent, and the like. However, the blends do not requireany stabilizers, anti-oxidants or the like to enable the blend towithstand the effects of irradiation and substantially maintainstructural integrity for a useful period after irradiation.

The process of blending known mixtures of polymers is well known tothose skilled in the art. The available methods of blending are welldescribed in the literature, such as, Mathews, Polymer MixingTechnology, Chapter 3 (Applied Science Publishers, Essex, England, 1982)incorporated herein by reference. In the case of the present invention,the method of blending involves the use of an extruder by feeding thepolymers (in the proper weight percentages) that had been dry-blendedtogether prior to the heated extrusion process.

The polymer blend can be extruded from the polymer melt in any shapewhich can be rapidly cooled to obtain the polymer blend. The shapeand/or thickness of the extruded material will be dependent on theefficiency of the quenching systems utilized. Generally, films and blownmicrofiber webs are the preferred extruded materials.

To obtain a polymer blend having non-crystalline mesomorphouspolypropylene contained therein, the extruded blend must be quenched ina manner such that primarily the mesomorphous phase of polypropylene isobtained. Miller, "On the Existence of Near-Range Order in IsotacticPolypropylenes," in Polymer, One 135 (1960) and in European PatentApplication 87304084.4, (EPO Publication 0248545), both of which arehereby incorporated by reference herein, disclose suitable methods knownto those skilled in the art for preparation of mesomorphouspolypropylene.

As described by these prior publications, various known methods ofquenching as soon as possible, and preferably immediately afterextrusion can be used to obtain a polymer blend having non-crystallinemesomorphous polypropylene. Quenching methods include plunging theextruded material into a cold liquid, for example, an ice water bath,spraying the extruded material with a liquid such as water, and/orrunning the extruded material over a cooled roll or drum. Extrudedpolymer blended film of the present invention is preferably quenchedimmediately after extrusion by contact with a quench roll or by plungingthe film into a quench bath. For a film thickness of from about 1.0 mil(0.025 mm) to about 10.0 mil (0.25 mm), where a quench roll is used,roll temperature is preferably maintained at a temperature below about24° C. and the film is generally in contact with the roll untilsolidified. The quench roll should be positioned relatively close to theextruder die, the distance being dependent on the roll temperature, theextrusion rate, the film thickness, and the roll speed. Generally, thedistance from the die to the roll is about 0.1 in. (0.25 cm) to 2 in. (5cm). Where a quench bath is used, the bath temperature is preferablymaintained at a temperature below about 40° F. (4° C.). The bath shouldbe positioned relatively close to the die, generally about 0.1 in. (0.25cm) to 5 in. (13 cm) from the die to the bath.

Melt blown microfibers of polymer blends of this invention are producedby extruding molten polymer through a die into a high velocity hot airstream to produce fibers having an average fiber diameter of less thanabout 10 microns. The fibers are generally collected on a drum in theform of a web. The preparation of microfiber webs is described in ReportNo. 4364 of the Naval Research Laboratories, published May 25, 1954,entitled "Manufacture of Superfine Organic Fibers," by Wente, Van A. etal. and in Wente, Van A., "Superfine Thermoplastic Fibers" in IndustrialEngineering Chemistry, Vol. 48, No. 8, August, 1956, pp. 1342-1346, bothof which are incorporated herein by reference.

To achieve webs of the polymer blends of the invention, the blownmicrofiber web is preferably quenched by spraying with a liquid such aswater or by cooling the collector drum onto which the microfiber web iscollected. Optimum quenching can be achieved by spraying the fiber webnear the die, then collecting the web on a cooled drum. The water sprayis preferably at a temperature of less than about 50° F. (10° C.) andless than about 1 inch (2.5 cm) from the die and the collector drum ispreferably about 2 inches (5 cm) to 4 inches (10 cm) from the die, butcan be as much as 8 inches (20 cm) to 10 inches (25 cm) depending onextrusion rates.

The extruded polymer blend should not be subjected to any treatment,such as orientation or stretching, at temperatures above about 60° C.because such treatment would transform the polymer blend to a structurepredominantly containing crystalline polypropylene.

The polymer blends of the invention can withstand irradiation bysterilizing ionizing radiation such as gamma radiation. The dosage ofgamma radiation is generally desirably in the range from about 0.1 Mrad(1.0 kGy) to about 10 Mrad (100 kGy) and preferably in the range fromabout 1.0 Mrad (10 kGy) to about 6.0 Mrad (60 kGy) for sterilization ofmedical articles.

The following non-limiting examples are provided to further illustratethe invention.

EXAMPLES 1-5

Polypropylene (Cosden 8771, melt index=9) and polybutylene (Shell 0400,melt index=20), with a variation of weight percentage by weight shown inTable I for Examples 2-4 were blended by dry blending in the respectiveweight percentages and then fed into the extrusion hopper of a 5.1 cm (2Inch) Rheotec Extruder. The polybutylene of Example 1 was not dryblended prior to extrusion. The extruder was operated at a flow rate of9.08 kg/hr, having a screw speed of 20 rpm and temperature zones asfollows: Zone 1: 216° C.; Zones 2-4: 244° C.; Die Zone: 244° C. toassure a melt temperature of 244° C. These Examples 1-4 were extrudedinto four mil (0.102 mm.) films on a chrome plated casting role in whichthe quench temperature was controlled at 54° F. (12.2° C. ) in order forExamples 2-4 to control the non-crystalline mesomorphous structure ofthe polypropylene in the blend.

Example 5 was prepared by polypropylene films being extruded from ExxonPP-3014 polypropylene polymer (melt flow index - 12; average molecularweight, by GPC: 161,000) using a 11/4 inch (3.2 cm) Brabender extruderwith a 12 inch (30.5 cm) wide film die at a thickness of about 1.5 mil(0.04 mm) under the following conditions:

    ______________________________________                                        Melt temperature (°C.)                                                                     203                                                       Screw speed (rpm)    40                                                       Polymer flow rate (kg/hr)                                                                          5                                                        Die temperature (°C.)                                                                      204                                                       ______________________________________                                    

The films were extruded onto a chrome-plated 3 inch (7.6 cm) diametercasting roll spaced 1 inch (2.5 cm) from the die. The film was incontact with the roll for about 2.5 seconds. The roll was maintained at6.7° C.

The crystalline structure of each Example 1-5 the blend, or absence,thereof, was determined by wide-angle x-ray diffraction (WAXD). For eachweight fraction Examples 1-5 there is a corresponding wide-angle x-raydefraction graph in the FIGS. 2-6, respectively. The very sharp peaks inthe WAXD graph demonstrates the high crystallinity weight fraction ofpure polybutylene in FIG. 1 prepared according to Example 1. As theweight fraction of the polybutylene decreases in Examples 2-4, the lesspronounced excitation peaks in the WAXD graphs of FIGS. 3-5 demonstratethe decreased relative crystallinity in the polymer blend.

Samples of each film of Examples 1b, 1c, 2b, 2c, 3b, 3c, 4b, 4c, and 5bwere irradiated with gamma rays using a cobalt 60 (Co60) source indosages indicated in Table I. Tensile properties were measured on bothirradiated and unirradiated films of the various examples at varioustimes to study the aging effects of the polymer blend and consequentdegradation caused by the irradiation. Tensile measurements wereperformed on an Instron 1122 unit using a 2 inch×1/2 inch sample size ata strain test rate of one hundred percent (100%) per minute (2 inchesper minute) and using the ASTM D882-31 procedure.

Each of the Examples 1-5 was measured for percent elongation at breakusing ASTM D882-31 procedure, the results of which are tabulated inTable I.

                                      TABLE I                                     __________________________________________________________________________    Percent Elongation at Break of Compatible Polymer Blends With and Without     Irradiation                                                                   PB/PP        Irradiation                                                                           % Elongation at Break After                              Example                                                                            Weight Percent                                                                        Dosage (kGy)                                                                          0 mths.                                                                            2 mths.                                                                            3 mths.                                                                            4 mths.                                                                           5 mths.                                                                           6 mths.                                                                            9 mths.                      __________________________________________________________________________    1a   100/0    0      200  --   200  --  --  200  200                          1b   100/0   30      200  200  200  180 150 150  125                          1c   100/0   60      200  150  130   75  45  25   0                           2a   75/25    0      270  --   270  --  --  270  270                          2b   75/25   30      270  270  270  270 270 270  270                          2c   75/25   60      270  270  270  270 250 240  270                          3a   50/50    0      370  --   350  --  --  410  390                          3b   50/50   30      370  370  370  370 390 380  340                          3c   50/50   60      370  360  400  360 360 370  410                          4a   25/75    0      500  --   500  --  --  500  500                          4b   25/75   30      500  500  520  500 510 500  500                          4c   25/75   60      500  520  460  480 500 --   450                          5a*   0/100   0      420  >400 >400 --  --  >400 --                           5b*   0/100  30      >400 >400 >400 --  --  >400 --                           __________________________________________________________________________

The polymers of polybutylene and non-crystalline mesomorphouspolypropylene are compatible polymers and form an excellent blend in abroad range of mixtures according to the objects of the presentinvention. Polybutylene and mesomorphous polypropylene are clearlycompatible polymers because the blends throughout the range of mixingexhibit a greater percent elongation at break value than hypotheticallinear value at the same blend weight fraction as calculated accordingto the equation described in the Summary of the Invention above. As seenin FIG. 1, the actual measured percent elongation at break value exceedsthe hypothetical linear value for each of Examples 2a, 3a, and 4a.Further, Example 4a has an even greater percent elongation at breakvalue than mesomorphous polypropylene homopolymer. Thus, a blend ofpolybutylene as the compatible polymer is within the scope of thepresent invention throughout at least nearly the entire range ofpossible weight fractions.

When subjected to a moderate dose of gamma radiation, polybutylene ofExample 1 begins to degrade within four months after irradiation. Whensubjected to more extreme radiation, the polybutylene of Example 1begins degrading within two months. Hence, polybutylene alone is not asuccessful candidate for medical packaging requiring any significantstorage time between irradiation and use.

A blend of mesomorphous polypropylene with polybutylene throughout theweight fractions shown in Examples 2-4, demonstrates substantialmaintenance of structural integrity and resistance to irradiationdegradation at dosages as much as 6.0 Mrad (60 kGy). Indeed, the blendsof Examples 3a-c and 4a-c compare favorably in this respect with puremesomorphous polypropylene of Example 5a-b. This result indicates theblends of this invention appreciably lose none of the radiationresistance provided by mesomorphous polypropylene while providingthrough careful choice(s) of compatible polymer the packaging propertiesmesomorphous polypropylene clearly lacks. The blends substantiallymaintain their structural integrity for useful storage periods, evenafter irradiation.

Having determined the desired available useful duration of resistance tosterilization irradiation, and then choosing various other propertiessuch as puncture resistance, tear strength and the like desired for theblend as a medical packaging article, one can obtain an acceptable blendwithin the scope of the present invention.

Yield and break tensile strengths are also indicative of desirablepackaging property of tear strength. Table II demonstrates the same fiveExamples where yield tensile strength and break tensile strength aremeasured at irradiation dosages of 6 Mrad (60kGy) for a period up tonine months.

                                      TABLE II                                    __________________________________________________________________________    Irradiated Compatible Polymer Blend Tensile Strength                                            Irradiation at 60 kGy                                                                     Irradiation at 60 kGy                           WAXD      PB/PP   Yield Tensile (kg/cm.sup.2)                                                               Break Tensile (kg/cm.sup.2)                     Example                                                                            Figure                                                                             Weight Percent                                                                        t = 0                                                                              t = 9 mths.                                                                          t = 0                                                                              t = 9 mths.                                __________________________________________________________________________    1    2    100/0   309.34                                                                             *      323.40                                                                             *                                          2    3    75/25   154.67                                                                             146.94 316.37                                                                             308.64                                     3    4    50/50   144.83                                                                             153.26 284.73                                                                             274.19                                     4    5    25/75   202.48                                                                             213.02 246.07                                                                             240.44                                     5    6     0/100  175.76                                                                             182.79 186.31                                                                             199.67                                     __________________________________________________________________________     *Too brittle to measure.                                                 

The data of Table II indicate substantial maintenance of tensilestrength for the blends of Examples 2-4 for at least nine months afterirradiation and better irradiated break tensile strength of such blendsover the tensile strength of mesomorphous polypropylene of Example 5under the same irradiated conditions.

Break tensile strength of the mesomorphous polypropylene homopolymer ofExample 5 is the lowest of all Examples. Conversely, break tensilestrength for polybutylene homopolymer of Example 1 is the highest andoccurs immediately after irradiation at 6 Mrad (60 kGy). Degradation ofpolybutylene homopolymer nine months later is too severe even to allowmeasurement of the tensile strength. Thus, break tensile strength of theblends of Examples 2-4 increases with increasing polybutylene weightfraction, and the break tensile strength of these blends issubstantially maintained for at least nine months after irradiation at 6Mrad (60 kGy). Unexpectedly, the tensile strength of mesomorphouspolypropylene destined for irradiation will be improved when suchpolypropylene is blended with a compatible polymer that alone suffersdegradation from such irradiation.

A polymer blend of mesomorphous polypropylene and polybutylene exhibitsthe property of resistance to sterilization irradiation exclusivelyfound in mesomorphous polypropylene and exhibits the break tensilestrength predominantly found in polybutylene, even after exposure tosterilization radiation, which would otherwise embrittle thepolybutylene homopolymer. Moreover, because low molecular weightpolymers, e.g., polybutylene are well known in the art as being punctureresistant, having good tear strength and being capable of being heatsealed to like materials, its presence in the polymer blend encouragesthe blend to be used in applications where such packaging properties arerequired.

EXAMPLES 6-10

Medical articles or their packaging often require manufacture or closureby heat sealing a film to itself or against another material. A polymerblend possessing resistance to structurally destructive forms ofsterilization should demonstrate acceptable heat sealability.

Examples 6-10 were tested for their heat sealability, againstthemselves, respectively, or other similar useful heat sealablematerials.

Table III below demonstrates how blends of the present invention respondto heat sealing strength tests when heat sealed to other materialsincluding themselves. Crystalline polypropylene heat seal tear strengthis provided for comparison purposes.

Examples 6-10 were prepared in a similar manner as those of Examples 1-5using a 2 Inch Berlyn Extruder operated at a flow rate of 9.08 kg/hr,having a screw speed of 37 rpm and a Die Temperature of 221° C. toassure a melt temperature of 221° C. The blends were extruded into 3.5mil (0.089 mm) films on a role chilled to 32° F. (0° C.). Thecrystalline polypropylene was prepared by using bi-axial orientationmethods under elevated temperature conditions.

Each of the films were tested by heat sealing such samples usingpressures of 40 pounds per square inch (2.8122 kg/cm²) for 4 seconds to:

(1) a 3.0 mil (0.0765 mm) film made from low density polyethylene (LDPE)(available from Quantum Resin and branded as NPE 963-2PE) at 210° C.;

(2) a film of CoTran Controlled Caliper ethylene vinyl acetate (EVA),MSP98793, (available from Minnesota Mining and Manufacturing Company ofSt. Paul, Minn.) at 210° C.;

(3) a film of Celgard 2400 microporous polypropylene membrane availablefrom Hoescht-Celanese Corporation at 199° C.; and

(4) to another sample of the same film (self) at 199° C.

Then, each of the films were placed in an Instron 1122 machine tomeasure tear strength of the heat sealed portions of the samples.Constantly increasing force was applied to pull an unsealed portion ofeach sample at a 90° angle from the heat sealed portion. The heat sealstrength data in Table III show the forces at which the heat seals beganto fail.

                  TABLE III                                                       ______________________________________                                                       Heat Seal Test Strength                                        PB/PP          (grams/cm)                                                     Example                                                                              Weight Percent                                                                            LDPE    EVA    Celgard                                                                              Self                                 ______________________________________                                        6      100/0        5       18     693   1155                                 7      60/40       27      331    1129   1143                                 8      50/50       27      255    1233   1005                                 9      40/60       25      281    1362   1278                                 10      0/100      13      317     746   1407                                 Crystalline polypropylene                                                                    13      229       161    16                                    ______________________________________                                    

The heat seal tear strength of each of Examples 6-10 to other samples ofthe same respective Example (self) is significantly high to merit usingpolymer blends of the present invention in packaging and other useswhich requires heat sealing of two pieces of the same material together.Also, the blends of Examples 7-9 compare favorably with polybutylenehomopolymer and mesomorphous polypropylene homopolymer, in that the heatseal tear strength of the blends is not significantly lower than therespective heat seal tear strengths of the homopolymers of Examples 6and 10. By comparison the heat seal tear strength of crystallinepolypropylene is negligible.

With respect to LDPE heat seal tear strength, none of the Examples 6-10is significantly high to be universally useful as a heat seal candidatewith LDPE. However, of the Examples, the blends of Examples 7-9 havehigher heat seal tear strength than the homopolymers of Examples 6 and10 or crystalline polypropylene and may be useful for specific packagingpurposes where easier heat seal release is needed.

With respect to Celgard heat seal tear strength, the blends of Examples7-9 are excellent, stronger than either the polybutylene or mesomorphouspolypropylene homopolymer films of Examples 6 and 10 and much strongerthan crystalline polypropylene. The polymer blends of the presentinvention are excellent candidates as films to be heat sealed to filmsof Celgard; a well known and versatile commercial material.

With respect to EVA, the blends of Examples 7-9 compare favorably withmesomorphous polypropylene homopolymer of Example 10 and crystallinepolypropylene, which surprisingly have better heat seal tear strengthsthan the polybutylene homopolymer of Example 6. The blends of Examples7-9 are useful in being heat sealed to EVA.

The heat seal tear strength of mesomorphous polypropylene homopolymercompares favorably with or exceeds the heat seal strength ofpolybutylene homopolymer. Whereas, crystalline polypropylene has notgenerally been used in the medical packaging art in heat sealableapplications, mesomorphous polypropylene may be useful. However,mesomorphous polypropylene otherwise lacks other desirable packagingproperties such as tear strength and puncture resistance, which may beprovided by blending with compatible polymers such as polybutylene.

EXAMPLES 11-15

The polymer blends of the present invention have improved high speedpuncture resistance and tear strength when compared with mesomorphouspolypropylene and low density polyethylene (LDPE). The test used MTS 810materials testing unit from MTS Systems of Eden Prairie, Minn. andemploying testing procedures from ASTM number D3763. Establishing thepuncture rate at 7,700 inches per minute, a probe having a diameter of1.5 inches was impacted against an unsupported sample having a diameterof 5.0 inches (12.7 cm) for each of Examples 11-15 prepared in the samemanner as Examples 1-5 and LDPE prepared according to the methodindicated in footnote below Table IV.

The polymer blends of the present invention also exhibit improved tearstrength over mesomorphous polypropylene homopolymer. The test used theSingle Tear Test method, ASTM D-1938-67, which measures the force ingrams to propagate a tear across a film at a tear rate of 250 mm/min.The film samples for Examples 11-15 were 75 mm long by 25 mm wide,having a single slit 50 mm long 12.5 mm from the longer edge of thesample. Table IV shows the tear strength results.

                                      TABLE IV                                    __________________________________________________________________________    Improved High Speed Puncture Resistance                                                            Energy to                                                                              Tear Resistance                                        PB/PP   Thickness                                                                           Maximum Force                                                                          (Machine Direction)                             Example*                                                                             Weight Percent                                                                        (mm)  (Joules) g/cm of sample thickness)                       __________________________________________________________________________    11     100/0   0.096 1.678    122,000                                         12     75/25   0.114 1.167    63,000                                          13     50/50   0.109 0.897    26.900                                          14     25/75   0.124 0.891    14,200                                          15      0/100  0.102 0.430    10,800                                          Low Density    0.102 0.553    --                                              Polyethylene                                                                  (LDPE)**                                                                      __________________________________________________________________________     *Examples 11-15 prepared in the same manner and correspond respectively t     Examples 1-5.                                                                 **LDPE prepared from Dowlex 752 available from Dow Chemical Company of        Midland, Michigan in the same manner as the samples of Example 5.        

The data in Table IV demonstrate that the relatively thin films of thepolymer blends in various weight fractions have significantly improvedresistance to high speed punctures compared with mesomorphouspolypropylene homopolymer or another packaging material such as LDPE.Although the resistance to puncturing decreases as the weight fractionof polybutylene in the polymer blends of the present inventiondecreases, there is significantly improved high speed punctureresistance in the blends of Examples 12-14 over the resistance foundmesomorphous polypropylene homopolymer or LDPE homopolymer. The data inTable IV also demonstrates the improved tear strength of the blends ofExamples 12-14 over the tear strength of mesomorphous polypropylenehomopolymer of Example 15. Polybutylene homopolymer has excellent tearstrength as seen in Example 11, which contributes to the tear strengthof Examples 12-14, respectively.

Thus, while mesomorphous polypropylene has excellent radiationresistance and good heat sealability, it lacks the puncture resistanceand tear strength that polybutylene can contribute to the polymer blend.For packaging purposes, the weight fractions of the mesomorphouspolypropylene and the compatible polymer in the polymer blend may bedetermined by the relative balance of properties desired for the blend.

EXAMPLES 16-19

Other polymers compatible with mesomorphous polypropylene demonstratethe scope of the present invention. FIG. 7 is a graph analogous to thegraph of FIG. 1, recording the actual percent elongation at break valuesto demonstrate the compatibility with mesomorphous polypropylene withExxelor PA-23 available from Exxon Corporation, which is believed to bean ethylene-based elastomer. FIGS. 8-11 show the relative crystallineand non-crystalline morphologies for various polymer blends ofmesomorphous polypropylene and Exxelor PA-23.

That variety of blends of mesomorphous polypropylene (FINA 8771, meltindex=9) and Exxelor PA-23 having the weight percentages shown in TableV were extruded using a 2 Inch Rheotec Extruder operating at a flow rateof 9.08 kg/hr, a screw speed of 20 rpm and at a die zone temperature of232° C. to assure a melt temperature of 232° C. The blends were extrudedin four mil (0.10 mm) films on a chrome casting role in which thequenched temperature was controlled at a temperature less than about 22°C. in order to give a non-crystalline mesomorphous morphology for thepolypropylene.

Table V identifies the correlation of each of the Examples 16-19 to thewide-angle x-ray defraction FIGS. 8-11.

Table V also identifies the percentage elongation at break after each ofthe examples was sterilized in the same manner as that for Examples 1-5at 3, 6, and 10 Mrad (30, 60, and 100 kGy) sterilization doses,respectively. Storage time was extended for these Examples to twelvemonths.

The FIGS. 8-11 show decreasing relative crystallinity with increasingmesomorphous polypropylene weight fraction in the polymer blend.

Table V also provides the unirradiated, zero duration percent elongationat break data for each Example 16a, 17a, 18a, and 19a. The percentelongation at break for mesomorphous polypropylene is obtained fromExample 5. A percent elongation at break value of 639% for Exxelor PA-23was obtained by testing performed on the same size samples of 4.0 mil(0.102 mm) films according to the same testing procedures as thatdescribed for Examples 1-5. The graph in FIG. 7 shows that each Example16a, 17a, 18a, and 19a of the blend has a greater percent elongation atbreak value than the hypothetical linear value computed according to theequation described in the Summary of the Invention above. Thus, ExxelorPA-23 is another polymer which is compatible throughout at least nearlythe entire possible range of weight fractions for the polymer blend ofthe present invention.

                                      TABLE V                                     __________________________________________________________________________    Improved Radiation Resistance for Exxelor PA-23/PP                                    Exxelor                                                                             Irradiation                                                     WAXD    PA-23/PP                                                                            Dosage                                                                              % Elongation at Break After                               Ex.                                                                              Figure                                                                             Weight %                                                                            (kGy) 0 mths.                                                                           1 mth.                                                                            2 mths.                                                                           3 mths.                                                                           6 mths.                                                                           9 mths.                                                                           12 mths.                          __________________________________________________________________________    16a                                                                               8   80/20  0    669 --  --  --  --  --  700                               16b                                                                               8   80/20 30    --  637 590 671 627 843 683                               16c                                                                               8   80/20 60    --  612 622 625 593 723 758                               16d                                                                               8   80/20 100   --  597 601 617 587 594 --                                17a                                                                               9   60/40  0    649 --  --  --  --  --  693                               17b                                                                               9   60/40 30    --  599 616 622 654 820 667                               17c                                                                               9   60/40 60    --  594 655 678 612 644 745                               17d                                                                               9   60/40 100   --  580 628 610 644 708 715                               18a                                                                              10   40/60  0    622 --  --  --  --  --  630                               18b                                                                              10   40/60 30    --  620 571 644 610 611 613                               18c                                                                              10   40/60 60    --  590 617 633 616 611 694                               18d                                                                              10   40/60 100   --  601 589 615 581 598 605                               19a                                                                              11   20/80  0    580 --  --  --  --  --  590                               19b                                                                              11   20/80 30    --  560 535 587 672 635 605                               19c                                                                              11   20/80 60    --  563 526 623 617 594 585                               19d                                                                              11   20/80 100   --  559 464 616 588 541 618                               __________________________________________________________________________

The data in Table V show that even after subjected to irradiationdosages of as much as 10 Mrad (100 kGy), blends having compatibleExxelor PA-23 in weight percents from about twenty percent (20%) toabout eighty percent (80%) by weight of the polymer blend showsubstantial maintenance of structural integrity of the blend as long asone year, even after irradiation.

Indeed, any polymer compatible in a blend with mesomorphouspolypropylene having desired properties which are otherwise lacking inthe mesomorphous polypropylene homopolymer may be included within thescope of the present invention. The relative weight fractions of themesomorphous polypropylene and the polymer compatible therewith may bebalanced within that determined effective range of weight fractionsaccording to other desired physical properties provided by thecompatible polymer, such as additional heat sealing capability, impactresistance, tear strength, and the like.

COMPARISON EXAMPLES 20-25

It is important for the polymer blends of the present invention to beprepared under controlled temperature conditions. At the time ofextrusion, the polymer blends must be quenched at temperatures less thanfrom about 100° F. (38° C.). Otherwise, radiation resistance is lost.Table VI demonstrates the deleterious effect of extruding at a slowcooling temperature at about 130° F. (55° C.).

Examples 20-22 were prepared according to the same process as describedfor Examples 1-4 except that the cooling temperature was 130° F. (55°C.). Examples 23-25 were prepared according to the same process as forExamples 16-19 except that the cooling temperature at extrusion was 135°F. (57.2° C.). Examination of the crystallinity of the blends of each ofthe examples below in Table VI was made by wide angle x-ray diffraction.

                                      TABLE VI                                    __________________________________________________________________________                   PP    Irradiation                                                             Crystal                                                                             Dosage                                                                              % Elongation at Break After                        Ex.                                                                              Blend Weight %                                                                            Type  (kGy) 0 mths.                                                                           2 mths.                                                                           4 mths.                                                                           6 mths.                                                                           9 mths.                                                                           12 mths.                       __________________________________________________________________________    20a                                                                              PB/PP 75/25 *      0    280 --  --  310 270 --                             20b                                                                              PB/PP 75/25 *     30    280 280 250 240 200 --                             20c                                                                              PB/PP 75/25 *     60    280 200 120  40  10 --                             21a                                                                              PB/PP 50/50 Crystalline                                                                          0    400 --  --  410 380 --                             21b                                                                              PB/PP 50/50 Crystalline                                                                         30    400 400 370 310 270 --                             21c                                                                              PB/PP 50/50 Crystalline                                                                         60    400 300 270 220 100 --                             22a                                                                              PB/PP 25/75 Crystalline                                                                          0    500 --  --  480 500 --                             22b                                                                              PB/PP 25/75 Crystalline                                                                         30    500 500 500 450 420                                22c                                                                              PB/PP 25/75 Crystalline                                                                         60    500 --  --  400 150 --                             23a                                                                              PA-23/PP                                                                            80/20 Crystalline                                                                          0    681 --  --  --  --  662                            23b                                                                              PA-23/PP                                                                            80/20 Crystalline                                                                         30    --  440 --  100  55 --                             23c                                                                              PA-23/PP                                                                            80/20 Crystalline                                                                         60    --  410 --   71  21 10                             23d                                                                              PA-23/PP                                                                            80/20 Crystalline                                                                         100   --  225 --   37  12  5                             24a                                                                              PA-23/PP                                                                            40/60 Crystalline                                                                          0    628 --  --  --  --  632                            24b                                                                              PA-23/PP                                                                            40/60 Crystalline                                                                         30    --  575 --  250 150 40                             24c                                                                              PA-23/PP                                                                            40/60 Crystalline                                                                         60    --  540 --  170  80 20                             24d                                                                              PA-23/PP                                                                            40/60 Crystalline                                                                         100   --  500 --   80  15  7                             25a                                                                              PA-23/PP                                                                            20/80 Crystalline                                                                          0    642 --  --  --  --  635                            25b                                                                              PA-23/PP                                                                            20/80 Crystalline                                                                         30    --  610 --  410 200 65                             25c                                                                              PA-23/PP                                                                            20/80 Crystalline                                                                         60    --  580 --  200  70 21                             25d                                                                              PA-23/PP                                                                            20/80 Crystalline                                                                         100   --   40 --   13  11 11                             __________________________________________________________________________     *Not susceptible to determination                                        

As may be seen from examination of Table VI, the degradation of theblends over time increases with the increase in radiation dosage. All ofExamples 20-25 have lower percent elongation at break values withincreased irradiation dosages, longer duration, and both. However, whencomparing polymer blends of Examples 20-25 shown in Table VI with thepolymer blends of the present invention of Examples 2-4 and 16-19 atcomparable irradiation dosages for comparable storage times, the sameweight fractions comprising the blends when quenched during extrusion attemperatures less than about 38° C., and desirably less than about 24°C. resist the structural degradation effects of sterilizationirradiation.

The polymer blends of the present invention may be used for a variety ofmedical or other article or packaging constructions. Because the blendsare radiation resistant, films or microfiber webs made from the blendsand used as components in medical or other articles or packaging formedical or other articles are capable of maintaining their structuralintegrity over useful periods of article's shelf and use lives even ifsubjected to dosages of sterilizing irradiation. Because the blends areheat sealable, puncture resistant and have good tear strength, films ormicrofiber webs or fibrous webs made from the blends are versatilecomponents for an article or the packaging for an article.

Some utilizations will require radiation resistance; some utilizationswill require puncture resistance, tear strength, additional heatsealability, and the like; some will require both. The compatiblepolymer blends of the present invention can universally serve any ofthose utilizations even if not all of its benefits are fully beingutilized.

Various possible uses of films made from blends of the present inventioninclude packaging for medical articles, such as syringes, requiringsterilization during storage, backings for transdermal delivery patchesrequiring heat sealability and good tear strength and possible radiationresistance, and sidewalls for ostomy pouches requiring good tearstrength, puncture resistance, and heat sealability. This listing is notand should not be construed as exhaustive of the many possible uses ofthe blends of the present invention.

Films of the polymer blend of the present invention may desirably havean additional layer grafted to the film to enhance other properties suchas surface adhesion, permeability, coefficient of friction, or otherproperties desirable to those skilled in the art for the film. Forexample, not by way of limitation, surface adhesion is desirable inorder to provide the application of primers and other coatings to a filmthat would not otherwise adhere well to a film of the polymer blends ofthe present invention.

Using the methods identified in European Patent Publication EPO 0297741,which is incorporated by reference herein, the surface adhesion layer isdesirably grafted to the polymer blend by electron beam irradiation indosages of from about 0.5 Mrad (5 kGy) to about 20 Mrad (200 kGy) andpreferably about 5 Mrad (50 kGy). The compounds desirably to be graftedto the polymer blend film include acrylic acid (AA), dimethylacrylamide(DMA), N-vinyl-2-pyrrolidone (NVP), and a copolymer of NVP andtrimethylolpropanetriacrylate (NVP/TMPTA). Other possible compounds tobe used as a grafting layer include glycidyl acrylate, hydroxyethylacrylate, hydroxymethyl acrylate, 2-vinyl pyridine, sulfoethylmethacrylate, diisopropylacrylate, or N,N-diethylamino acrylate.

Exemplary compounds were grafted onto films prepared in the same manneras that for films of Examples 2 and 4. Grafting used an electron beamgenerating dosages identified in Table VII in a nitrogen atmosphere at175 kv with a web speed of 25 feet per minute (7.62 m/min).

The strength of the graft was measured using a 180° peel adhesion testdescribed as follows: A 2.5 cm wide, 20.3 cm long strip ofpressure-sensitive adhesive tape (Scotch™ brand tape no. 8411) isadhered to a 10.1 om wide, 15.2 cm long sheet of test substrate with afree end of the tape extending beyond the end of the test substrate. Thesample is rolled twice with a 1.35 kg hard rubber roller to ensurecontact between the adhesive and the test substrate. The sample is agedat room temperature (22° C.) for 24 hours. The free end of the tape isremoved from the test substrate at a rate of 6 inches/minute using aSlip/Peel Tester, available from Instrumentors, Inc.

Table VII displays the data for the grafted compound, its e-beamirradiation dosage, and peel adhesion results tested at variousintervals over at least 6 months time.

                                      TABLE VII                                   __________________________________________________________________________    Peel Adhesion Results on Graft Modified Polymer Blends                        Grafted    e-Beam   Peel Force (g/cm.)                                        Ex.                                                                              Monomer Irradiation (kGy)                                                                      1 month                                                                            3 months                                                                           7 months                                                                           9 months                                   __________________________________________________________________________    2  Control 50       138  124  --   146                                        2  AA      50       269  239  --   217                                        2  DMA     50       411  413  308  314                                        2  NVP     100      181  180  163  165                                        2  NVP/TMPTA                                                                             100      213  162  167  167                                        4  Control 50       147  185  --   161                                        4  AA      50       279  252  --   218                                        4  DMA     50       411  328  254  --                                         4  NVP     100      234  217  181  273                                        4  NVP/TMPTA                                                                             100      239  231  287  --                                         __________________________________________________________________________

Throughout the range of polymer blend weight fractions, a blend havingthe grafted monomer of any of the compounds identified above hasimproved surface adhesion for at least six months after sterilizationirradiation.

Table VIII compares the graft-modified polymer blends and the unmodifiedpolymer blends in respect of elongation at break after e-beamirradiation at the dosages shown in Table VIII.

                                      TABLE VIII                                  __________________________________________________________________________    % Elongation at Break Comparison                                              Grafted    e-Beam   % Elongation at Break                                     Ex.                                                                              Monomer Irradiation (kGy)                                                                      1 month                                                                            3 months                                                                           7 months                                                                           9 months                                   __________________________________________________________________________    2  Control 50       315  --   346  395                                        2  AA      50       323  --   347  361                                        2  DMA     50       308  --   349  317                                        2  NVP     100      310  311  382  386                                        2  NVP/TMPTA                                                                             100      314  309  365  388                                        4  Control 50       525  --   643  669                                        4  AA      50       438  --   458  638                                        4  DMA     50       442  --   583  664                                        4  NVP     100      431  489  687  603                                        4  NVP/TMPTA                                                                             100      423  561  598  624                                        __________________________________________________________________________

The various grafted-monomer polymer blends do not suffer degradation toe-beam irradiation. Combined with the radiation resistance of thepolymer blends described above, graft-modified polymer blendssubstantially maintain the structural integrity provided by the polymerblend of the present invention and have the benefit of the improvedsurface adhesion provided by the grafted-monomer layer.

While in accordance with the patent statutes, description of thepreferred weight fractions, processing conditions, and product usageshave been provided, the scope of the invention is not to be limitedthereto or thereby. Various modifications and alterations of the presentinvention will be apparent to those skilled in the art without departingfrom the scope and spirit of the invention. The examples described inthis application are illustrative of the possibilities of varying theamounts of polymer in the blend to achieve properties for specificpurposes.

Consequently, for an understanding of the scope of the presentinvention, reference is made to the following claims.

What is claimed is:
 1. A method for preparing a polymer blend,comprising:blending polypropylene and at least a discernible amount ofpolybutylene to form a polymer blend; extruding said polymer blend;quenching said extruded polymer blend immediately after said extrudingto provide a mesophorous polymer blend having non-crystallinemesomorphous polypropylene contained therein.
 2. A method for preparinga polymer blend according to claim 1, wherein said quenching occurs attemperatures less than about 38° C.
 3. A method for preparing a polymerblend according to claim 1, wherein said blending mixes polybutylene inan amount of from about one percent to about ninety-nine percent byweight of the weight of the polymer blend.
 4. A method for preparing apolymer blend according to claim 1, wherein said blending mixespolybutylene in an amount of from about five percent to aboutninety-five percent by weight of the weight of the polymer blend.
 5. Amethod for preparing a polymer blend according to claim 1, wherein saidblending mixes polybutylene in an amount of from about ten percent toabout ninety percent by weight of the weight of the polymer blend.
 6. Amethod for preparing a polymer blend according to claim 1, wherein saidblending mixes polybutylene in an amount of from about twenty percent toabout eighty percent by weight of the weight of the polymer blend.
 7. Amethod for preparing a polymer blend according to claim 1, wherein saidblending mixes polybutylene in an amount of from about twenty-fivepercent to about seventy-five percent by weight of the weight of thepolymer blend.
 8. A method for preparing a polymer blend according toclaim 1, wherein said blending mixes polybutylene in an amount of fromabout forty percent to about sixty percent by weight of the weight ofthe polymer blend.
 9. A method for preparing a polymer blend accordingto claim 1, wherein said blending mixes a minor amount of saidpolypropylene/with polybutylene.
 10. The method for preparing a polymerblend according to claim 1, wherein said quenching further comprisesforming a film of the polymer blend.
 11. The method for preparing apolymer blend according to claim 10, wherein said method furthercomprises after said forming of a film of the polymer blend, the step ofgrafting at least one monomer as a surface adhesion layer to said filmin the presence of electron beam irradiation in dosages of from about0.5 Mrad to about 20 Mrad.
 12. The method for preparing a polymer blendaccording to claim 11, wherein said surface adhesion layer comprisesacrylic acid, dimethylacrylamide, N-vinyl-2-pyrrolidone, a copolymer ofN-vinyl-2-pyrrolidone and trimethylolpropanetriacrylate, glycidylacrylate, hydroxyethyl acrylate, hydroxymethyl acrylate, 2-vinylpyridine, sulfoethyl methacrylate, diisopropylacrylate, or N,N-diaminoacrylate.